331 



The granites of the Newry district have been examined by 

 Mr. J. A. PHILLIPS.^) The " white " granite of Newry is, according to this 

 author, a compound of quartz, orthoclase and dark mica. The " blue 

 granite " of Goragh Wood contains in addition hornblende, plagioclase 

 and sphene. It is therefore a sphene- bearing hornblende-granitite. 

 Foreign inclusions and concretionary patches occur in this rock. 



North-west of Ireland. The gneissose granites of Donegal have 

 also been examined by Dr. HAUGHTOX. They are banded and the 

 general strike of the banding is about 10 or 15 S. of W. The 

 essential constituents are quartz, orthoclase, oligoclase and black mica. 

 White mica and hornblende are occasionally present. The accessory 

 minerals are sphene, tourmaline, beryl, garnet, molybdenite and copper 

 pyrites. Fifteen analyses are given. These show a much greater 

 variability in composition than those of the normal intrusive granites 

 of the east of Ireland. Some of the rocks analysed were of intermediate 

 composition. 



The microscopic characters of the granite of Galway, which is 

 also gneissose, have been described by Professor HuLL.< 3 > It is rendered 

 porphyritic by the occurrence of flesh-coloured orthoclase. The 

 principal constituents are orthoclase, microcline, oligoclase, quartz and 

 dark mica. Colourless mica occurs in twisted flakes. Normal intrusive 

 granite of uniform texture occurs in Co. Mayo. That of Aillemore (4) 

 is composed of quartz, orthoclase, microcline, oligoclase (?) and dark 

 green mica. It occasionally shows a graphic structure. 



A slide of gneissose granite from the neighbourhood of Galway, 

 in the author's possession, shows orthoclase, plagioclase, dark mica 

 hornblende, granulitic quartz, sphene and apatite. The granulation of 

 the quartz is probably the result of dynamic metamorphism. 



We have now to consider the Trachytic Rocks. Under this 

 head we include the felsites, quartz-felsites, liparites or rhyolites, 

 obsidians and pitchstones. These rocks occur as intrusive sheets, dykes 

 and lava-flows, and less frequently as irregular intrusive masses. It 

 is impossible to decide as to whether any particular rock is an 

 intrusive mass or a lava-flow by reference to petrographical char- 

 acters alone. The occurrence of a marked fluidal structure is, 

 however, more common in the lavas than in the intrusive rocks. 

 The acid lavas are distinguished from the basic lavas by a greater 

 want of homogeneity. They frequently exhibit a remarkable banded 

 or laminated structure in consequence of the variation in texture 

 and composition of successive layers. Very frequently the lamina are 

 crumpled and contorted in a most remarkable manner. These banded 

 structures are equally characteristic of both ancient and modern rocks 

 of similar composition. They are found in the ancient Ordovician 



(1) Q.J.G.S., Vol. XXXVI. (1880), p. 16. 



(2) Q.J.Q.S., Vol. XVIII., p. 408. 



(3) G.M., Decade I., Vol. X. (1873), p. 193. 



(4) HULL; Jour. Geol. Soc., Ireland, Vol. IV., p. 4. 



